Large amounts of metal components including, for example, nickel and vanadium are contained in the heavy oil such as the residue of the atmospheric distillation or the vacuum distillation. The metal components poison the hydrorefining catalyst which is used, for example, for the desulfurization, the denitrogenation, and the cracking, and the catalytic activity is deteriorated thereby. Therefore, a treatment is previously performed with a hydrorefining catalyst aimed for the demetallation (hereinafter referred to as “demetallation catalyst” as well).
When a catalyst, in which pores having pore diameters of not more than 50 nm occupy almost all of the pore volume, is used as the demetallation catalyst, if the demetallation activity is enhanced, then a large amount of metal is deposited or accumulated in the vicinity of pores disposed near to the outer surface of the catalyst, i.e., in the vicinity of pore inlets or openings, and the pore inlets or openings are closed thereby. Therefore, the metal deposition capacity (amount of metal capable of being deposited in the pores until the catalyst loses the activity) is decreased. On the contrary, the metal deposition capacity can be increased by using a so-called bimodal catalyst, i.e., a catalyst which has pores with pore diameters of not more than 50 nm and which also has pores with pore diameters of not less than 50 nm.
The present applicant has disclosed a method for forming and calcinating a powder of γ-alumina as a method for producing the catalyst as described above (International Patent Application PCT/JP99/06760). However, in this method, pseudo-boehmite is calcinated to produce a γ-alumina powder, the γ-alumina powder is formed, and then the calcination is performed again. Therefore, it is necessary to perform the two calcinating steps. The production steps are complicated, and the production cost is expensive. Alternatively, a bimodal catalyst can be also produced by mixing a pseudo-boehmite powder, for example, with microparticulate carbon and organic matters to perform forming, and then burning and removing the microparticulate carbon and the like during calcination. However, in the case of the production method as described above, the mechanical strength of the catalyst is insufficient in some cases.